There are good reasons that ornamental grasses have become popular in gardens so quickly. Ornamental grasses add texture, form, movement, and sound to a garden, in an array of subtle colors. They will look good all season long with minimal care. But deciding which one or two to include in your garden is a tough decision. There are so many attractive ornamental grasses to choose from.
Not all ornamental grasses are hardy in every zone, so checking that a grass will grow in your area will help you narrow down the field.
You will also want to be aware of whether the grass grows in a tidy clump or tends to spread. Another good place to begin making your ornamental grass selection is to first decide what purpose you want it to serve.
How to Use Ornamental Grasses in Your Garden Design
- Is it going to be a specimen plant? The vast majority of ornamental grasses will make great specimen plants or focal point. The decision then comes down to what grass has the foliage or form that will complement the rest of your garden. You may want a variegated leaf or one with a chartreuse or blue tint.
- Is winter interest a priority? Many gardeners like to leave their grasses standing throughout the winter. Grasses with stiffer leaves, like Switch Grass and Indian Grass, last longer than grasses with softer leaves, like Miscanthus.
- Are you looking for height? Some ornamental grasses spill over like fountains and some, like Indian Grass, stand straight and tall. Obviously, if you want an ornamental grass to give height to a garden, you are not going to select a dwarf variety or a low growing grass, such as Blue Fescue.
Aside from personal preferences and design needs, there are 2 major features to take into consideration: cool season versus warm season and growth habit (clumping vs. running).
Cool and Warm Season Ornamental Grasses
Dividing grasses into cool and warm season varieties is different than classifying them by USDA Hardiness Zones.
The zone ratings tell you if a grass will survive the winter in your area. When we talk about cool and warm season grasses, we’re referring to when they bloom.
- Cool Season Ornamental Grasses: Cool season grasses start growing early in spring, usually as soon as the temperature starts staying above freezing. Some are even evergreen and require minimal grooming and cutting back as they start growing again, at the start of the season. Very often cool season grasses have their most vibrant color while they are actively growing in the spring.
Cool season grasses flower shortly after summer arrives. Once they flower, foliage growth slows down. Although they can remain attractive for the rest of the summer, the color gradually fades. Cool season grasses are especially good for gardens with short growing seasons. In hot, dry conditions cool season ornamental grasses will go dormant.
Cool season ornamental grasses tend to need more frequent division than warm season grasses. If left unmaintained, they will die out in the center. Still, some of the most attractive ornamental grasses are cool season.
Examples of Cool Season Grasses: Autumn Moor Grass (Sesleria), Blue Fescue (Festuca glauca), Blue Oat Grass (Helictotrichon sempervirens), Feather Reed Grass (Calamagrostis), Tufted Hair Grass (Deschampsia cespitosa)
- Warm Season Ornamental Grasses: Warm season ornamental grasses are slow to emerge in the spring. Don’t be alarmed and think they’ve died off during the winter. Many warm season ornamental grasses don’t get going until after the spring bulbs have faded.
Since warm season ornamental grasses are late to emerge, they also flower later in the summer than their cool season cousins. Many will remain in bloom well into the fall.
Warm season grasses also handle the heat, humidity, and drought well. Many popular ornamental grasses are warm season.
Examples of Warm Season Grasses: Big Bluestem (Andropogon gerardii), Dropseed (Sporobolus heterolepis), Fountain Grass (Pennisetum), Indian Grass (Sorghastrum nutans), Little Bluestem (Schizachyrium scoparium), Maiden Grass (Miscanthus sinensis), Northern Sea Oats (Chasmanthium latifolium), Switch Grass (Panicum)
Growth Habits of Ornamental Grasses
- Clump Forming Ornamental Grasses
Clump forming ornamental grasses are favored by gardeners because they are less aggressive in the garden. Clumping grasses will expand and get larger over time, but they tend to stay in a neat mound, rather than spreading throughout the garden. Although some clump formers will also self-seed, they rarely become invasive.
Examples of Clump Forming Grasses: Fescue (Festuca), Miscanthus, Fountain Grass (Pennisetum), Maiden Grass (Miscanthus sinensis), Switch Grass (Panicum)
Ornamental Grasses that Run
Unlike the tidy growth habit of clump-forming grasses, ornamental grasses that increase by rhizomes will spread, or run, throughout a garden bed and can quickly take over. Their growth habit is a lot like turf grass. While you want turf grass to spread and become a lawn, this type of growth habit is not suited to a garden border.
On the other hand, ornamental grasses with a running habit can make good ground covers, if you want to fill in a large area or stabilize a slope. Grasses such as Liriope (Liriope spicata) and Mondo grass (Ophiopogon japonicus) are often used as ground covers. Just give them lots of room and don’t turn your back on them.
Growing rhizome spreading grasses in containers is a good option if you want to include one in your garden, without fear of it becoming invasive.
Examples of Runners: Blue Lyme Grass (Elymus arenarius), Ribbon Grass (Phalaris arundinacea) and many varieties of Calamagrostis and Carex.
Some ornamental grasses will stand tall and other have a fountain effect. These qualities will play a hand in how you use them in your garden design, but the main growth habits you should be concerned with when choosing an ornamental grass are whether it is a clump former or a runner.
Ornamental grasses should be clearly labeled as to whether they are clumpers or runners and whether they bloom in the cool or warm season. After that, it’s a matter of choosing an ornamental grass that’s compatible with your growing conditions and gardening style.